Photoelectric cell and process for producing metal oxide semiconductor film for use in photoelectric cell

ABSTRACT

A photoelectric cell that includes a first insulating base, having on its surface a first electrode layer, which has on its surface a metal oxide semiconductor film, which includes anatase titanium oxide particles, on which a photosensitizer is adsorbed and a second insulating base having on its surface a second electrode layer and an electrolyte sealed between the metal oxide semiconductor film and the second electrode layer. The first electrode layer and the second electrode layer are arranged opposite from each other. At least one of the first and second insulating bases with an electrode layer is transparent.

BACKGROUND OF THE INVENTION

The present invention relates to a photoelectric cell, a coating liquidfor forming a metal oxide semiconductor film for use in a photoelectriccell and a process for producing a metal oxide semiconductor film foruse in a photoelectric cell. More particularly, the present invention isconcerned with a photoelectric cell wherein the adsorption and carryingamounts of photosensitizer on a metal oxide semiconductor film are largeand the strength of bonding of the photosensitizer to the metal oxidesemiconductor film is large with the result that the photoelectric cellexhibits enhanced photoelectric transfer efficiency. Further, thepresent invention is concerned with a coating liquid for forming a metaloxide semiconductor film for use in such a photoelectric cell and aprocess for producing a metal oxide semiconductor film for use in such aphotoelectric cell.

A photoelectric transfer material is a material from which light energyis continuously taken out as electric energy and a material whichconverts light energy to electric energy by the utilization ofelectrochemical reaction between electrodes. When the photoelectrictransfer material is irradiated with light, electrons are generated fromone electrode. The electrons move to a counter electrode, and theelectrons having reached the counter electrode return by moving as ionsthrough an electrolyte to the one electrode. This energy conversion iscontinuously carried out, so that it is utilized in, for example, asolar cell.

The common solar cell consists of an electrode formed by coating thesurface of a support such as glass plate with transfer conductive film,wherein semiconductor for photoelectric transfer material is formed onthe transfer conductive film, a counter electrode formed by coating thesurface of a support such as a glass plate with another transparentconductive film, and an electrolyte sealed between these electrodes.

When this solar cell is irradiated with sunlight, the photosensitizerincorporated therein absorbs visible radiation region to thereby excitethe electrons of photosensitizer dye. The excited electrons move to thesemiconductor for photoelectric transfer material, and then thetransparent conductive glass electrode, further move to the counterelectrode. The electrons having reached the counter electrode reduce theoxidation-reduction system present in the electrolyte. On the otherhand, the photosensitizer having caused electrons to move to thesemiconductor becomes oxidized form. This oxidized form is reduced bythe oxidation-reduction system (which becomes reduced form) of theelectrolyte to thereby return to the original form. In this manner,electrons continuously flow. Therefore, functioning as the solar cellcomprising the semiconductor for photoelectric transfer material can berealized by virtue of the continuous flow of electrons.

A semiconductor having a surface on which a photosensitizer exhibitingabsorption in visible radiation region is adsorbed is used as such aphotoelectric transfer material. For example, Japanese Patent Laid-openPublication No. 1(1989)-220380 describes a solar cell comprising a metaloxide semiconductor and, superimposed on a surface thereof, a layer of aphotosensitizer such as a transition metal complex. Further, PublishedJapanese Translation of PCT Patent Applications from Other States, No.5(1993)-504023 describes a solar cell comprising a titanium oxidesemiconductor layer doped with metal ions and, superimposed on a surfacethereof, a layer of a photosensitizer such as a transition metalcomplex.

In these solar cells, for increasing the photoelectric transferefficiency, it is important that the move of electrons from thephotosensitizer layer having absorbed light and having been excited to atitania film be performed rapidly. When the move of electrons is notperformed rapidly, the electrons recombine with the transition metalcomplex such as a ruthenium complex to thereby invite the problem ofcausing a drop of photoelectric transfer efficiency. Therefore, studies,such as on the improvement of the condition of bonding of thephotosensitizer to the titania film surface and the improvement ofelectron mobility within the titania film, are performed.

For improving the condition of bonding of the photosensitizer to thetitania film surface, for example, it has been proposed to, at the timeof forming a metal oxide semiconductor film, repeat the operations ofapplication of titania sol to a base, drying and annealing to therebyform a porous thick film, thus rendering the semiconductor film porous,with the result that the amount of Ru complex carried on the surface isincreased. Further, it has been proposed to carry out an annealing at400° C. or higher to thereby sinter fine particles of titania with theresult that a conductivity enhancement is realized. Still further, inPublished Japanese Translation of PCT Patent Applications from OtherStates, No. 6(1994)-511113, it is carried out in order to increase theeffective surface of the semiconductor to, after the formation of asemiconductor layer composed of a porous titanium oxide, immerse thesemiconductor layer in an aqueous solution of titanium chloride, or toelectrochemically deposit titanium oxide on the porous titanium oxidesemiconductor layer with the use of a solution of titanium chloridehydrolyzate.

However, in the current state of the art, there are problems, forexample, when annealing is effected for increasing the electronmobility, sintering occurs to thereby decrease the porosity (effectivesurface) with the result that the adsorption amount of photosensitizeris lowered. Moreover, because the photoelectric transfer efficiency isnot satisfactory, the use thereof is limited. Therefore, there is ademand for further improvement of the solar cells.

An object of the present invention is to provide a photoelectric cellwherein the adsorption proportion of photosensitizer is high, thereactivity of photosensitizer is high, electron, movement is smoothwithin the semiconductor and, hence, the photoelectric transferefficiency is enhanced. Another object of the present invention is toprovide a coating liquid for forming a metal oxide semiconductor filmfor use in such a photoelectric cell. A further object of the presentinvention is to provide a process for producing a metal oxidesemiconductor film for use in such a photoelectric cell.

SUMMARY OF THE INVENTION

A photoelectric cell of the present invention (hereinafter referred toas “the first photoelectric cell”) comprises:

an insulating base having on its surface an electrode layer (1), theelectrode layer (1) having on its surface a metal oxide semiconductorfilm (2) on which a photosensitizer is adsorbed;

an insulating base having on its surface an electrode layer (3), theelectrode layer (1) and the electrode layer (3) arranged opposite toeach other; and

an electrolyte sealed between the metal oxide semiconductor film (2) andthe electrode layer (3),

wherein:

at least one of the electrode-having insulating bases is transparent;and

the metal oxide semiconductor film (2) comprises anatase titanium oxideparticles.

It is preferred that the anatase titanium oxide particles have acrystallite diameter ranging from 5 to 50 nm. It is also preferred thatthe anatase titanium oxide particles be colloid particles having anaverage particle diameter ranging from 5 to 600 nm. These anatasetitanium oxide particles are preferably those obtained by subjectingperoxotitanic acid to heating and aging.

Another form of photoelectric cell of the present invention (hereinafterreferred to as “the second photoelectric cell”) comprises:

an insulating base having on its surface an electrode layer (1), theelectrode layer (1) having on its surface a metal oxide semiconductorlayer (2) on which a photosensitizer is adsorbed;

an insulating base having on its surface an electrode layer (3), theelectrode layer (1) and the electrode layer (3) arranged opposite toeach other; and

an electrolyte sealed between the metal oxide semiconductor layer (2)and the electrode layer (3),

wherein:

conductive protrusions (4) jutting from the surface of the electrodelayer (1) exist, the metal oxide semiconductor layer (2) formed so as tocover the conductive protrusions (4) and the electrode layer (1), and

at least one of the electrode-layer-having insulating bases istransparent.

It is preferred that the metal oxide semiconductor layer be formed alonga contour of the conductive protrusions (4). It is also preferred thatthe metal oxide semiconductor layer comprise spherical particles of atleast one of metal oxides selected from the group consisting of titaniumoxide, lanthanum oxide, zirconium oxide, niobium oxide, tungsten oxide,strontium oxide, zinc oxide, tin oxide and indium oxide. These sphericalparticles preferably have an average particle diameter ranging from 5 to600 nm.

In particular, the spherical particles are preferably those composed ofanatase titanium oxide or those having a core-shell structure comprisinga core particle of 0.1 to 500 nm in average particle diameter having itssurface covered with a shell. It is preferred that the shell of thespherical particles of the core-shell structure be composed of anatasetitanium oxide. This anatase titanium oxide is preferably one obtainedby subjecting peroxotitanic acid to heating and aging as mentionedabove.

The metal oxide semiconductor layer of each of the first photoelectriccell and second photoelectric cell according to the present inventionpreferably contains a titanium oxide binder. This metal oxidesemiconductor layer is preferably one obtained by implanting ions of atleast one gas selected from the group consisting of O₂, N₂, H₂ and inertgases of Group 0 of the periodic table and thereafter annealing.Further, it is preferred that the metal oxide semiconductor layer have apore volume of 0.05 to 0.8 ml/g and an average pore diameter of 2 to 250nm.

The coating liquid for forming a metal oxide semiconductor film for usein a photoelectric cell according to the present invention comprisesperoxotitanic acid, anatase titanium oxide particles and a dispersionmedium. The anatase titanium oxide particles are preferably thoseobtained by subjecting peroxotitanic acid to heating and aging.

The process for producing a metal oxide semiconductor film for use in aphotoelectric cell according to the present invention comprises applyingthe above coating liquid for forming a metal oxide semiconductor filmfor use in a photoelectric cell to thereby obtain a coating film andhardening the coating film. In this process for producing a metal oxidesemiconductor film for use in a photoelectric cell, the hardening of thecoating film is preferably performed by irradiating the coating filmwith ultraviolet light. The coating film, after the hardening byultraviolet light irradiation, may be subjected to implantation of ionsof at least one gas selected from the group consisting of O₂, N₂, H₂ andinert gases of Group 0 of the periodic table and thereafter annealing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view of one form of the firstphotoelectric cell according to the present invention.

FIG. 2 is a schematic sectional view of another form of the firstphotoelectric cell according to the present invention.

FIG. 3 is a schematic sectional view of one form of the secondphotoelectric cell according to the present invention.

FIG. 4 is an enlarged sectional view of one form of conductiveprotrusion contour.

FIG. 5 is an enlarged sectional view of one form of conductiveprotrusion contour.

FIG. 6 is a schematic sectional view of another form of the secondphotoelectric cell according to the present invention.

FIG. 7 is a schematic sectional view of a further form of the secondphotoelectric cell according to the present invention.

FIG. 8 is a schematic view showing the definition of the thickness ofmetal oxide semiconductor layer disposed in the second photoelectriccell.

DESCRIPTION OF SIGN CHARACTER

1: electrode layer,

2: metal oxide semiconductor film,

3: transparent electrode layer,

4: electrolyte,

5: insulating base,

6: transparent insulating base,

11: electrode layer,

12: metal oxide semiconductor layer,

13: transparent electrode layer,

14: conductive protrusions,

15: electrolyte,

16: insulating base, and

17: transparent insulating base.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will now be described in detail.

First Photoelectric Cell

The first photoelectric (photovoltanic) cell of the present inventioncomprises:

an insulating base having on its surface an electrode layer (1), theelectrode layer (1) having on its surface a metal oxide semiconductorfilm (2) on which a photosensitizer is adsorbed;

an insulating base having on its surface an electrode layer (3), theelectrode layer (1) and the electrode layer (3) arranged opposite toeach other; and

an electrolyte sealed between the metal oxide semiconductor film (2) andthe electrode layer (3), wherein:

at least one of the electrode-having insulating bases is transparent;and

the metal oxide semiconductor film (2) comprises anatase titanium oxideparticles.

This photoelectric cell is, for example, one shown in FIG. 1.

FIG. 1 is a schematic sectional view of one form of photoelectric cellaccording to the present invention. It comprises:

an insulating base 5 having on its surface an electrode layer 1, theelectrode layer 1 having on its surface a metal oxide semiconductor film2 on which a photosensitizer is adsorbed;

an insulating base 6 having on its surface a transparent electrode layer3, the electrode layer 1 and the electrode layer 3 arranged opposite toeach other; and

an electrolyte 4 sealed between the metal oxide semiconductor film 2 andthe electrode layer 3.

Insulating bases can be used without any particular limitation as theinsulating base 5 as long as they possess insulating properties.

Bases which are transparent and possess insulating properties, such as aglass plate and a base of PET or other polymers, can be used astransparent insulating base 6.

The electrode layer 1 on a surface of the insulating base 5 can becomposed of common electrodes such as those of tin oxide, tin oxidedoped with Sb, F or P, indium oxide doped with Sn and/or F, antimonyoxide and platinum.

The transparent electrode layer 3 superimposed on a surface of thetransparent insulating base 6 can be composed of common transparentelectrodes such as those of tin oxide, tin oxide doped with Sb, F or P,indium oxide doped with Sn and/or F and antimony oxide. These electrodelayers 1 and 3 can be formed on the respective insulating bases by theuse of conventional methods such as the pyrolytic method and the CVDmethod.

The insulating base 5 may be transparent like the transparent insulatingbase 6. Also, the electrode layer 1 may be a transparent electrode likethe transparent electrode layer 3.

It is preferred that the visible radiation transmission through thetransparent insulating base 6 and the transparent electrode layer behigh. For example, it is preferred that the visible radiationtransmission be 50% or over, especially 90% or over. When the visiblelight transmission is lower than 50%, the photoelectric transferefficiency may be unfavorably low.

The value of resistance of each of the electrode layer 1 and electrodelayer 3 is preferably 10 Ω/cm² or less. When the electrode layerresistance is higher than 10 Ω/cm², the photoelectric transferefficiency. may be unfavorably low.

Metal Oxide Semiconductor Film

The metal oxide semiconductor film 2 is formed on the electrode layer 1provided on the surface of the insulating base 5. The metal oxidesemiconductor film 2 may be formed on the transparent electrode layer 3provided on the surface of the transparent insulating base 6, as shownin FIG. 2. FIG. 2 is a schematic sectional view of another form ofphotoelectric cell according to the present invention. Like signcharacters are used through FIGS. 1 and 2.

The thickness of this metal oxide semiconductor film 2 is preferably inthe range of 0.1 to 50 μm.

Anatase titanium oxide particles are contained in the metal oxidesemiconductor film 2.

The anatase titanium oxide particles, as compared with other metal oxideparticles, exhibit a high adsorption proportion of photosensitizer and ahigh electron mobility within the semiconductor film and haveadvantageous properties such as high stability, high safety and easyfilm formation.

It is preferred that the above anatase titanium oxide particles have acrystallite diameter ranging from 5 to 50 nm, especially 7 to 30 nm. Thecrystallite diameter of the anatase titanium oxide particles can bedetermined by measuring the half-value width of peak ascribed to face(1.0.1) by X-ray analysis and calculating from the measured width withthe use of the Debye-Scherrer formula. When the crystallite diameter ofthe anatase titanium oxide particles is less than 5 nm, the electronmobility within the particles is decreased. On the other hand, when thecrystallite diameter is larger than 50 nm, the adsorption amount ofphotosensitizer is reduced. Therefore, in both instances, thephotoelectric transfer efficiency may be unfavorably low.

The anatase titanium oxide particles can be obtained by conventionalmethods, for example, the method in which hydrous titanic acid gel orsol is prepared by, for example, the sol gel technique and, after theaddition of an acid or alkali according to necessity, the gel or sol isheated and aged.

Also, the anatase titanium oxide particles for use in the presentinvention can be obtained by first adding hydrogen peroxide to hydroustitanic acid gel or sol so that the hydrous titanic acid is dissolvedtherein and converted to peroxotitanic acid, subsequently adding analkali, preferably ammonia and/or an amine, to the peroxotitanic acid soas to render the same alkaline and thereafter heating and aging at 80 to350° C. Further, the anatase titanium oxide particles for use in thepresent invention can be obtained by adding the obtained anatase colloidparticles as seed particles to peroxotitanic acid and repeating theabove operations. Highly crystalline anatase titanium oxide colloidparticles shown by X-ray diffraction can be obtained in this method ofgrowing seed particles.

The terminology “peroxotitanic acid” refers to titanium peroxidehydrate. This titanium peroxide exhibits absorption in the visibleradiation region, and can be prepared by adding hydrogen peroxide to atitanium compound such as titanium hydride, a titanium alkoxide ortitanic acid, or to hydrous titanic acid gel or sol, followed by heatingif necessary.

Sol or gel of hydrous titanium acid can be obtained by adding an acid oralkali to an aqueous solution of a titanium compound to thereby effect ahydrolysis, if necessary followed by washing, heating and aging. Theemployable titanium compound, although not particularly limited, can be,for example, a titanium salt such as a titanium halide or titanylsulfate, a titanium alkoxide such as a tetraalkoxytitanium, or atitanium compound such as titanium hydride.

It is especially preferred that the anatase titanium oxide particles foruse in the present invention be those obtained by adding an alkali toperoxotitanic acid and heating and aging the mixture.

The above anatase titanium oxide particles are preferably in the form ofcolloid particles having an average particle diameter of 5 to 600 nm.The diameter of the anatase titanium oxide particles can be measured byLaser Doppler type particle diameter measuring instrument (manufacturedby NIKKISO CO., LTD.: microtrack). When the average particle diameter ofthe anatase titanium oxide particles is less than 5 nm, it may occurthat the formed metal oxide semiconductor film is likely to have cracks,thereby rendering it difficult to form a crackless thick film having athickness mentioned later by a small number of coating operations.Further, it may occur that the pore diameter and pore volume of themetal oxide semiconductor film are reduced to thereby cause theadsorption amount of photosensitizer to unfavorably decrease. On theother hand, when the average particle diameter of the anatase titaniumoxide particles is larger than 600 nm, it may occur that the strength ofthe metal oxide semiconductor film is unsatisfactory.

The metal oxide semiconductor film 2 generally contains a titanium oxidebinder component together with the above anatase titanium oxideparticles.

This titanium oxide binder component can be, for example, a titaniumoxide composed of hydrous titanic acid gel or sol obtained by thesol-gel technique or the like, or an amorphous titanium oxide bindersuch as a decomposition product of a peroxotitanic acid which isobtained by adding hydrogen peroxide to hydrous titanic acid gel or solso that the hydrous titanic acid is dissolved. Of these, thedecomposition product of a peroxotitanic acid is especially preferablyused.

This titanium oxide binder component forms a dense homogeneousadsorption layer on the surface of anatase titanium oxide particles. Byvirtue of this adsorption layer, the obtained metal oxide semiconductorfilm can have an increased adherence to the electrode. Further, the useof the above titanium oxide binder component causes the mutual contactof anatase titanium oxide particles to change from a point contact to aface contact with the result that not only can the electron mobility beenhanced but also the adsorption amount of photosensitizer can beincreased.

In the metal oxide semiconductor film 2, the weight ratio, in terms ofTiO₂, of titanium oxide binder component to anatase titanium oxideparticles (titanium oxide binder component/anatase titanium oxideparticles) is preferably in the range of 0.05 to 0.50, still preferably0.1 to 0.3. When the weight ratio is less than 0.05, it may occur thatthe absorption of visible radiation is unsatisfactory and that theadsorption amount of photosensitizer cannot be increased. On the otherhand, when the weight ratio is higher than 0.50, it may occur that nodense semiconductor film is obtained. Further, it may occur that theelectron mobility is not enhanced.

In the metal oxide semiconductor film 2, the pore volume is preferablyin the range of 0.05 to 0.8 ml/g, and the average pore diameter ispreferably in the range of 2 to 250 nm. When the pore volume is smallerthan 0.05 ml/g, the adsorption amount of photosensitizer is likely to beunfavorably small. On the other hand, when the pore volume is largerthan 0.8 ml/g, it may occur that the electron mobility within the filmis decreased to thereby lower the photoelectric transfer efficiency.Also, when the average pore diameter is smaller than 2 nm, theadsorption amount of photosensitizer is likely to be unfavorably small.On the other hand, when the average pore diameter is larger than 250 nm,it may occur that the electron mobility is decreased to thereby lowerthe photoelectric transfer efficiency.

This metal oxide semiconductor film 2 can be prepared from the followingcoating liquid for forming a metal oxide semiconductor film.

Coating Liquid for Forming a Metal Oxide Semiconductor Film

The coating liquid for forming a metal oxide semiconductor filmaccording to the present invention comprises peroxotitanic acid, anatasetitanium oxide particles and a dispersion medium.

Peroxotitanic acid can be prepared by adding hydrogen peroxide to anaqueous solution of a titanium compound, or sol or gel of titanium oxidehydrate, and heating the mixture.

Sol or gel of titanium oxide hydrate can be obtained by adding an acidor alkali to an aqueous solution of a titanium compound to therebyeffect a hydrolysis, if necessary followed by washing, heating andaging. The employable titanium compound, although not particularlylimited, can be, for example, a titanium salt such as a titanium halideor titanium sulfate, a titanium alkoxide such as a tetraalkoxytitanium,or a titanium compound such as titanium hydride.

The anatase titanium oxide particles can be obtained by conventionalmethods, for example, the method in which hydrous titanic acid gel orsol is prepared by, for example, the sol-gel technique and, after theaddition of an acid or alkali according to necessity, the gel or sol isheated and aged.

Also, the anatase titanium oxide particles for use in the presentinvention can be obtained by first adding hydrogen peroxide to hydroustitanic acid gel or sol so that the hydrous titanic acid is dissolvedtherein and converted to peroxotitanic acid, subsequently adding analkali, preferably ammonia and/or an amine, to the peroxotitanic acid soas to render the same alkaline and thereafter heating and aging at 80 to350° C. Further, the anatase titanium oxide particles for use in thepresent invention can be obtained by adding the obtainable anataseparticles as seed particles to peroxotitanic acid and repeating theabove operations.

In the present invention, especially, those obtained by adding an alkalito peroxotitanic acid and heating and aging the mixture are preferablyused as the anatase titanium oxide particles.

It is preferred that the above anatase titanium oxide particles have acrystallite diameter ranging from 5 to 50 nm, especially 7 to 30 nm.Further, the anatase titanium oxide particles are preferably in the formof colloid particles having an average particle diameter of 5 to 600 nm.When the average particle diameter of the anatase titanium oxideparticles is less than 5 nm, it may occur that the formed metal oxidesemiconductor film is likely to have cracks, thereby rendering itdifficult to form a crackless thick film having a thickness mentionedlater by a small number of coating operations. Further, it may occurthat the pore diameter and pore volume of the metal oxide semiconductorfilm are reduced to thereby cause the adsorption amount ofphotosensitizer to unfavorably decrease. On the other hand, when theaverage particle diameter of the anatase titanium oxide particles islarger than 600 nm, it may occur that the strength of the metal oxidesemiconductor film is unsatisfactory.

In the coating liquid for forming a metal oxide semiconductor film foruse in a photoelectric cell according to the present invention, theweight ratio, in terms of TiO₂, of peroxotitanic acid to anatasetitanium oxide particles (peroxotitanic acid/anatase titanium oxideparticles) is preferably in the range of 0.05 to 0.50, still preferably0.1 to 0.3. When the weight ratio is less than 0.05, it may occur thatthe absorption of visible-region light is unsatisfactory and that theadsorption amount of photosensitizer cannot be increased. On the otherhand, when the weight ratio is higher than 0.50, it may occur that nodense semiconductor film is obtained. Further, it may occur that theelectron mobility is not enhanced.

The above peroxotitanic acid and anatase titanium oxide particles arepreferably contained in the coating liquid for forming a metal oxidesemiconductor film for use in a photoelectric cell in a concentration of1 to 30% by weight, still preferably 2 to 20% by weight, in terms ofTiO₂.

The employed dispersion medium is not particularly limited as long asthe peroxotitanic acid and titanium oxide particles can be dispersedtherein and the dispersion medium can be removed by drying. Inparticular, alcohols are preferred.

Furthermore, if necessary, a film formation auxiliary may be containedin the coating liquid for forming a metal oxide semiconductor film foruse in a photoelectric cell according to the present invention. The filmformation auxiliary can be, for example, any of polyethylene glycol,polyvinylpyrrolidone, hydroxypropylcellulose, polyacrylic acid andpolyvinyl alcohol. When the film formation auxiliary is contained in thecoating liquid, the viscosity of the coating liquid is increased tothereby enable obtaining a uniformly dried film. Further, the anatasetitanium particles are densely packed in the metal oxide semiconductorto thereby increase the bulk density. Thus, the metal oxidesemiconductor film exhibiting high adherence to the electrode can beobtained.

Process for Producing a Metal Oxide Semiconductor Film for use in aPhotoelectric Cell

The above metal oxide semiconductor film for use in a photoelectric cellcan be produced by applying the above coating liquid for forming a metaloxide semiconductor film for use in a photoelectric cell onto theelectrode layer on a base or base surface, drying the applied coatingand hardening the dried coating film.

The coating liquid is preferably applied in such an amount that thethickness of the finally formed metal oxide semiconductor film is in therange of 0.1 to 50 μm. With respect to the application method, thecoating liquid can be applied by conventional methods such as thedipping, spinner, spray, roll coater and flexographic printing methods.

The drying temperature is not limited as long as the dispersion mediumcan be removed.

The thus formed coating film is preferably hardened by, generally,irradiating the same with ultraviolet light. The ultraviolet lightirradiation is performed in such a dose as required for decomposition ofperoxotitanic acid and hardening, although varied depending on, forexample, the content of peroxotitanic acid. When the film formationauxiliary is contained in the coating liquid, heating may be performedafter the hardening of the coating film to thereby decompose the filmformation auxiliary.

In the present invention, it is preferred that, after the hardening ofthe coating film by ultraviolet light irradiation, the coating film beirradiated with ions of at least one gas selected from among O₂, N₂, H₂,neon, argon, krypton and other inert gases of Group 0 of the periodictable and thereafter annealed.

With respect to the ion irradiation, it can be accomplished by theemployment of known methods such as the method of infiltrating a fixedamount of boron or phosphorus to a fixed depth in a silicon wafer at thetime of manufacturing IC and LSI. The annealing is performed by heatingat 200 to 500° C., preferably 250 to 400° C., for a period of 10 min to20 hr.

By virtue of the above gas ion irradiation, a multiplicity of defectsare formed at the surface of titania particles without the remaining ofions within the titanium oxide film. Moreover, the crystallinity ofanatase crystals after annealing is enhanced, and the mutual joining ofparticles is promoted. Therefore, not only is the bonding strengththereof with the photosensitizer increased but also the adsorptionamount of photosensitizer is augmented. Furthermore, the enhancement ofanatase crystallinity and the promotion of particle joining increase theelectron mobility. Consequently, the photoelectric transfer efficiencycan be enhanced.

The thickness of the thus obtained metal oxide semiconductor film ispreferably in the range of 0.1 to 50 μm.

In the photoelectric cell of the present invention, the metal oxidesemiconductor film 2 has a photosensitizer adsorbed thereon.

The photosensitizer is not particularly limited as long as it is capableof absorbing visible radiation region and/or infrared radiation regionradiation to thereby excite itself. For example, an organic dye or ametal complex can be used as the photosensitizer.

Common organic dyes having, in the molecules thereof, functional groupssuch as carboxyl, hydroxyalkyl, hydroxyl, sulfone and carboxyalkylgroups can be used as the above organic dye. Examples of organic dyeinclude metal-free phthalocyanines, cyanine dyes, metalocyanine dyes,triphenylmethane dyes, and xanthene dyes such as uranine, eosine, RoseBengale, Rhodamine B and dibromofluorescein. These organic dyes arecharacterized in that the adsorption velocity on the metal oxidesemiconductor film is high.

On the other hand, as the metal complex, metal phthalocyanines such ascopper phthalocyanine and titanylphthalocyanine; chlorophyll; hemin;ruthenium cis-diaqua-bipyridyl complexes such as ruthenium tris(2,2′-bispyridyl-4,4′-dicarboxylate),cis-(SCN⁻)-bis(2,2′-bipyridyl-4,4′-dicarboxylato) ruthenium andruthenium cis-diaqua-bis (2,2′-bipyridyl-4,4′-dicarboxylate); porphyrinsuch as zinc tetra (4-carboxyphenyl) porphine; and ruthenium, osmium,iron and zinc complexes such as iron hexacyanide complex, as describedin, for example, Japanese Patent Laid-open Publication No.1(1989)-220380 and Japanese Translation of PCT Patent Applications fromOther States, No. 5(1993)-504023, can be used. These metal omplexes haveexcellent spectral sensitization effect and high durability.

The above organic dyes and metal complexes may be used eitherindividually or in mixture, and, further, the organic dyes can be usedin combination with the metal complexes.

The method of adsorbing these photosensitizers is not particularlylimited. For example, a solution in which a photosensitizer is dissolvedis adsorbed into the metal oxide semiconductor film by means of thecustomary method such as the dipping, spinner or spray method andthereafter dried. If necessary, the absorbing operation can be repeated.Alternatively, the photosensitizer solution, while being heated andrefluxed, is brought into contact with the above base having the metaloxide semiconductor film so that the photosensitizer can be adsorbed onthe metal oxide semiconductor film.

The solvent for dissolving photosensitizers is not limited as long as itis capable of dissolving them. For example, any of water, alcohols,toluene, dimethylformamide, chloroform, ethylcellosolve,N-methylpyrrolidone and tetrahydrofuran can be used.

The amount of photosensitizer adsorbed on the metal oxide semiconductorfilm is preferably 50 μg or more per cm² of specific surface area of themetal oxide semiconductor film. When the amount of photosensitizer isless than 50 μg, it may occur that the photoelectric transfer efficiencyis unsatisfactory.

The photoelectric cell of the present invention is fabricated by firstarranging the electrode-furnished insulating bases so that the metaloxide semiconductor film 2 is opposite to the transparent electrodelayer 3 (when the metal oxide semiconductor film 2 is superimposed onthe transparent electrode layer 3 as shown in FIG. 2, arrangement ismade so that the metal oxide semiconductor film 2 is opposite to theelectrode layer 1), subsequently sealing the side faces with a resin orthe like and thereafter charging an electrolyte 4 between theelectrodes.

A mixture of an electrochemically active salt and at least one compoundcapable of forming an oxidation-reduction system therewith is used asthe electrolyte 4.

The electrochemically active salt can be, for example, a quaternaryammonium salt such as tetrapropylammonium iodide. The compound capableof forming an oxidation-reduction system therewith can be, for example,any of quinone, hydroquinone, iodide (I⁻/I₃ ⁻), potassium iodide,bromide (Br⁻/Br₃ ⁻) and potassium bromide.

In the present invention, if necessary, a solvent can be added to theelectrolyte 4 so that the electrolyte 4 has the form of a solution. Theadded solvent is preferably one wherein the photosensitizer solubilityis low to such an extent that the photosensitizer adsorbed on the metaloxide semiconductor film is not desorbed and dissolved in the solvent.The solvent can be, for example, any of water, alcohols, oligoethers,carbonates such as propione carbonate, phosphoric esters,dimethylformamide, dimethylsulfoxide, N-methylpyrrolidone,N-vinylpyrrolidone, sulfur compounds such as sulfolane 66, ethylenecarbonate and acetonitrile.

The described first photoelectric cell of the present invention ensureshigh electron mobility within the semiconductor film to thereby beexcellent in photoelectric transfer efficiency, because thesemiconductor film containing anatase titanium oxide particles capableof having a large amount of photosensitizer adsorbed thereon is formedin the photoelectric cell.

Second Photoelectric Cell

The second photoelectric (photovoltanic) cell of the present inventioncomprises:

an insulating base having on its surface an electrode layer (i), theelectrode layer (i) having on its surface a metal oxide semiconductorlayer (ii) on which a photosensitizer is adsorbed;

an insulating base having on its-surface an electrode layer (iii), theelectrode layer (i) and the electrode layer (iii) arranged opposite toeach other; and

an electrolyte sealed between the metal oxide semiconductor layer (ii)and the electrode layer (iii),

wherein:

conductive protrusions (iv) jutting from the surface of the electrodelayer (i) exist, the metal oxide semiconductor layer (ii) formed so asto cover the conductive protrusions (iv) and electrode layer (i), and

at least one of the electrode-layer-having insulating bases istransparent.

An example of this photoelectric cell is one shown in FIG. 3.

FIG. 3 is a schematic sectional view of one form of the secondphotoelectric cell according to the present invention. The secondphotoelectric cell comprises:

an insulating base 16 having on its surface an electrode layer 11, theelectrode layer 11 having on its surface conductive protrusions 14jutting therefrom, a metal oxide semiconductor layer 12 on which aphotosensitizer is adsorbed being formed so as to cover the conductiveprotrusions 14 and the electrode layer (i);

a transparent insulating base 17 having on its surface a transparentelectrode layer 13, the electrode layer 11 and the electrode layer 13arranged opposite to each other; and

an electrolyte 15 sealed between the metal oxide semiconductor layer 12and the transparent electrode layer 13.

The insulating base 16 is not particularly limited as long as itpossesses insulating properties. The same insulating bases as mentionedwith respect to the first photoelectric cell can be employed.

Also, the same bases which are transparent and possess insulatingproperties, such as a glass plate and a base of PET or other polymers,as mentioned with respect to the first photoelectric cell can beemployed as the transparent insulating base 17.

The electrode layer 11 on the surface of the insulating base 16 and theconductive protrusions 14 jutting from the surface of the electrodelayer 11 can be composed of common conductive materials such as tinoxide, tin oxide doped with Sb, F or P, indium oxide doped with Snand/or F, antimony oxide and platinum. The electrode layer 11 and theconductive protrusions 14 may be composed of the same conductivematerial or may be composed of different conductive materials.

The configuration of the conductive protrusions is not limited to thecuboid structure shown in FIG. 3, and the conductive protrusions mayhave, for example, a net or band structure.

The electrode layer 11 is electrically connected with the conductiveprotrusions 14. The method of forming the electrode layer 11 and theconductive protrusions 14 is not particularly limited. The formationthereof can be accomplished by, for example, the method in which anelectrode film is superimposed on the insulating base by the pyrolytictechnique, the CVD technique, the vapor deposition technique or thelike, subsequently a resist is applied onto a surface of the electrodefilm, thereafter patterning for the conductive protrusions 14 is carriedout, and finally the resist is etched.

After the formation of the electrode layer 11 by the CVD technique, thevapor deposition technique or the like, a conductive particle layer maybe formed by applying a coating liquid containing conductive particlescomposed of the above conductive materials to thereby provide theconductive protrusions 14. The formation of protrusions in this mannerenables providing those of a net structure as shown in FIG. 4.Alternatively, the conductive protrusions 14 can be formed by applying acoating liquid containing conductive particles composed of a conductivematerial to thereby provide a conductive particle layer of closestpacking, subsequently coating a layer surface with a resist, thereafterperforming patterning for the conductive protrusions 14, and finallyetching the resist (see FIG. 5).

The individual conductive protrusions 14 are preferably positioned witha spacing therebetween which is at least twice the average thickness ofthe metal oxide semiconductor layer 12. The height of the conductiveprotrusions 14 is preferably in the range of 20 to 98% of the thicknessof the metal oxide semiconductor layer including the conductiveprotrusions 14. When the height falls within this range, the electronswithin the metal oxide semiconductor layer rapidly move to the electrodelayer 11 without recombining with the photosensitizer, so that thephotoelectric transfer efficiency of the photoelectric cell can beenhanced. When the height is less than 20%, the effect of increasing thevelocity of electron move to the electrode layer 11 is unsatisfactory.On the other hand, when the height is greater than 98%, it may occurthat the conductive protrusions may be electrically connected with theelectrolyte.

The transparent electrode layer 13 formed on the surface of thetransparent insulating base 17 can be composed of transparent electrodessuch as those of tin oxide, tin oxide doped with Sb, F or P, indiumoxide, indium oxide doped with Sn and/or F and antimony oxide. Thistransparent electrode layer 13 can be formed by the use of conventionalmethods such as the pyrolytic method, the CVD method and the vapordeposition method.

It is preferred that the visible light transmission through theinsulating base 16 and the electrode layer 13 be high, for example, 50%or more, especially 90% or more. When the visible light transmission isless than 50%, the photoelectric transfer efficiency is unfavorably low.

In the photoelectric cell of the present invention, it is requisite thatat least one of the pair of electrode-layer-having insulating bases betransparent. Therefore, the photoelectric cell is not limited to thestructure of FIG. 3. For example, referring to FIG. 6, transparentconductive protrusions 14 may be formed on the surface of thetransparent electrode layer 13 on transparent insulating base 17.Furthermore, all of the insulating bases 16 and 17, electrode layers 11and 13 and conductive protrusions 14 may be transparent.

It is generally preferred that the value of resistance of each of theabove electrode layers 11 and 13 and conductive protrusions 14 be 50Ω/cm² or less. When the electrode layer resistance is higher than 50Ω/cm², also, the photoelectric transfer efficiency may be unfavorablylow.

In the photoelectric cell of the present invention, the metal oxidesemiconductor layer 12 is formed so as to cover the electrode layer 11and conductive protrusions 14.

The metal oxide semiconductor layer 12 may have the conductiveprotrusions 14 buried therein, or may be formed along a contour of theelectrode layer 11 and conductive protrusions 14.

It is especially preferred that the metal oxide semiconductor layer beformed along a contour of the electrode layer 11 and conductiveprotrusions 14, as shown in FIG. 7. In this structure, not only does theelectrolyte infiltrate in the metal oxide semiconductor layer to therebyincrease the area of contact of the electrolyte with the metal oxidesemiconductor layer, but also the quantity of light incident on themetal oxide semiconductor layer and the adsorption amount ofphotosensitizer are increased. As a result, the photoelectric transferefficiency can be enhanced.

The thickness of the metal oxide semiconductor layer including theconductive protrusions 14 is preferably in the range of 0.1 to 500 μm.The thickness of the metal oxide semiconductor layer superimposed on theconductive protrusions or electrode layer surface is preferably in therange of 0.1 to 50 μm.

The average thickness of the metal oxide semiconductor layer refers tothe average of thickness of the metal oxide semiconductor layerincluding conductive protrusions, as illustrated in FIG. 8. The filmthickness of the metal oxide semiconductor layer refers to the thicknessof the metal oxide semiconductor layer on the electrode layer andconductive protrusion surface. The depth of infiltration of theelectrolyte in the metal oxide semiconductor layer (depth of electrolyteinfiltration) is preferably in the range of 20 to 90% of the thicknessof the metal oxide semiconductor layer. When the depth of electrolyteinfiltration is less than 20%, the effect of increasing the quantity ofincident light is not satisfactory. On the other hand, when it exceeds90%, it may occur that the strength of the metal oxide semiconductorlayer is unsatisfactory.

It is preferred that the metal oxide semiconductor layer comprisespherical particles of a metal oxide such as titanium oxide, lanthanumoxide, zirconium oxide, niobium oxide, tungsten oxide, strontium oxide,zinc oxide, tin oxide or indium oxide.

These metal oxide spherical particles preferably have an averageparticle diameter ranging from 5 to 600 nm. In the use of sphericalparticles, a uniform pore structure depending on particle diameter canbe formed when the particles are closely packed. Further, in the use ofspherical particles, a uniform surface condition is obtained. Therefore,the electron move from the photosensitizer to the metal oxidesemiconductor layer can efficiently be carried out with the result thatthe electron mobility is enhanced. The diameter of the metal oxideparticles can be measured by Laser Doppler type particle diametermeasuring instrument (manufactured by NIKKISO CO., LTD.: microtrack).When the average particle diameter of the metal oxide particles is lessthan 5 nm, it may occur that the formed metal oxide semiconductor layeris likely to have cracks, thereby rendering it difficult to form acrackless metal oxide semiconductor layer by a small number of coatingoperations. Further, it may occur that the pore diameter and pore volumeof the metal oxide semiconductor layer are reduced to thereby cause theadsorption amount of photosensitizer to unfavorably decrease. On theother hand, when the average particle diameter of the metal oxideparticles is larger than 600 nm, it may occur that the strength of themetal oxide semiconductor layer is unsatisfactory.

It is preferred that these metal oxide spherical particles be composedof anatase titanium oxide as described with respect to the firstphotoelectric cell.

In the second photoelectric cell of the present invention, sphericalparticles having a core-shell structure comprising a metal oxide coreparticle of 0.1 to 500 nm in average particle diameter having itssurface covered with a shell composed of the above metal oxide can alsobe preferably used as the metal oxide spherical particles. With respectto the spherical particles having a core-shell structure, the coreparticle, although not particularly limited as long as it is spherical,preferably consists of silica or the like from which particles ofperfect sphere can be easily obtained. Further, with respect to themetal oxide particles having a core-shell structure, the shell iscomposed of the above metal oxide, preferably titanium oxide, stillpreferably anatase titanium oxide.

The spherical particles having a core-shell structure can be obtained byslowly adding peroxotitanic acid to a dispersion of core particles whosediameter falls within the above range, if necessary, while heating.

When the particles per se are composed of anatase titanium oxide, orwhen the shell of particle having the core-shell structure is composedof anatase titanium oxide, as compared with particles composed of othermetal oxides, the adsorption amount of photosensitizer is large, theelectron mobility from the photosensitizer to the metal oxidesemiconductor and the electron mobility within the metal oxidesemiconductor layer are high, and there can be realized advantageousproperties such as high stability, high safety and easy film formation.

The metal oxide semiconductor layer may contain a binder componenttogether with the above spherical particles of metal oxide.

The same binder component as mentioned with respect to the firstphotoelectric cell can be employed in this metal oxide semiconductorlayer.

When anatase titanium oxide particles or spherical particles having acore-shell structure wherein the shell is composed of anatase titaniumoxide are used as the spherical particles, the use of a product ofhydrolysis/condensation polymerization of peroxotitanic acid as thebinder component enables forming a dense homogeneous adsorption layer onthe surface of anatase titanium oxide particles. Thus, the obtainedmetal oxide semiconductor layer enables increasing the adherence to theelectrode. Further, by using such a peroxotitanic acid as the bindercomponent changes the mutual contact of anatase titanium oxide particlesis changed from a point contact to a surface contact, thereby enablingenhancing the electron mobility.

In the metal oxide semiconductor layer, the weight ratio, in terms ofoxide, of binder component to metal oxide spherical particles (bindercomponent/metal oxide spherical particles) is preferably in the range of0.05 to 0.7, still preferably 0.1 to 0.5. When the weight ratio is lessthan 0.05, it may occur that the strength of the metal oxidesemiconductor layer is unsatisfactory and that the adherence of themetal oxide semiconductor layer to the electrode is not satisfactory. Onthe other hand, when the weight ratio is higher than 0.7, it may occurthat the diameter of formed pores is so small that the electron deliverybetween the electrolyte and the photosensitizer tends to be restrictedwith the result that the photoelectric transfer efficiency cannot beenhanced.

In the metal oxide semiconductor layer, the pore volume is preferably inthe range of 0.05 to 0.8 ml/g, and the average pore diameter ispreferably in the range of 2 to 250 nm. When the pore volume is smallerthan 0.05 ml/g, the adsorption amount of photosensitizer is likely to beunfavorably small. On the other hand, when the pore volume is largerthan 0.8 ml/g, it may occur that the electron mobility within the layeris decreased to thereby lower the photoelectric transfer efficiency.Also, when the average pore diameter is smaller than 2 nm, theadsorption amount of photosensitizer is likely to be unfavorably small.On the other hand, when the average pore diameter is larger than 250 nm,it may occur that the electron mobility is decreased to thereby lowerthe photoelectric transfer efficiency.

This metal oxide semiconductor layer can be formed by applying a coatingliquid for forming a metal oxide semiconductor layer for use in aphotoelectric cell, which comprises metal oxide spherical particles anda dispersion medium together with a binder according to necessity, anddrying the applied coating liquid.

The employed dispersion medium is not particularly limited as long asthe metal oxide particles and binder component can be dispersed thereinand the dispersion medium can be removed by drying. In particular,alcohols are preferred.

Furthermore, if necessary, a film formation auxiliary may be containedin the coating liquid. The film formation auxiliary can be, for example,any of polyethylene glycol, polyvinylpyrrolidone,hydroxypropylcellulose, polyacrylic acid and polyvinyl alcohol.

When the film formation auxiliary is contained in the coating liquid,the viscosity of the coating liquid is increased to thereby enableobtaining a uniformly dried layer. Further, the spherical particles aredensely packed. Thus, the metal oxide semiconductor layer exhibitinghigh adherence to the electrode can be obtained. The same coating liquidas used in the first photoelectric cell is also suitable to thisphotoelectric cell.

The coating liquid is preferably applied in such an amount that thethickness of the finally formed metal oxide semiconductor layer is inthe range of 0.1 to 50 μm. With respect to the application method, thecoating liquid can be applied by conventional methods such as thedipping, spinner, spray, roll coater and flexographic printing methodsand transferring method.

The drying temperature is not limited as long as the dispersion mediumcan be removed. When peroxotitanic acid is contained as the bindercomponent, if necessary, the dried layer may further be irradiated withultraviolet light to thereby harden the peroxotitanic acid. Theultraviolet light irradiation is performed in such a dose as requiredfor decomposition and hardening of peroxotitanic acid, although varieddepending on, for example, the content of peroxotitanic acid. When thefilm formation auxiliary is contained in the coating liquid, heating maybe performed after the hardening to thereby decompose the film formationauxiliary.

In the same manner as in the production of the first photoelectric cell,the thus formed metal oxide semiconductor layer may be subjected toimplantation of ions of at least one gas selected from among O₂, N₂, H₂,neon, argon, krypton and other inert gases of Group 0 of the periodictable and thereafter annealing.

In the second photoelectric cell, a photosensitizer is adsorbed on themetal oxide semiconductor layer in the same manner as in the firstphotoelectric cell.

The same photosensitizer as in the first photoelectric cell can be used.The method of adsorbing the photosensitizer is not particularly limited,and the photosensitizer can be adsorbed in the same manner as mentionedwith respect to the first photoelectric cell. The adsorption amount ofphotosensitizer on the metal oxide semiconductor layer is preferably 100μg or more per 1 cm² of specific surface area of the metal oxidesemiconductor layer. When the amount of photosensitizer is less than 100μg, it may occur that the photoelectric transfer efficiency isunsatisfactory.

In the same manner as mentioned with respect to the first photoelectriccell, the second photoelectric cell of the present invention isfabricated by first arranging the electrode-furnished insulating basesso that the metal oxide semiconductor layer 12 is opposite to thetransparent electrode layer 13, subsequently sealing the side faces witha resin or the like and thereafter charging an electrolyte between theelectrodes.

The same electrolyte as mentioned with respect to the firstphotoelectric cell can be used as the electrolyte 15.

In the described second photoelectric cell of the present invention, thespecified conductive protrusions are formed on the electrode surface.Thus, generated electrons can rapidly move to the electrode. Theelectrons do not recombine with the photosensitizer. Moreover, in thisphotoelectric cell, the adsorption proportion of photosensitizer ishigh, and moving of generated electrons is smooth. Therefore, the secondphotoelectric cell of the present invention is excellent inphotoelectric transfer efficiency.

The present invention enables obtaining the photoelectric cell whichensures high photoelectric transfer efficiency and is hence applicableto various photoelectric transfer uses.

Further, the metal oxide semiconductor film which is excellent inphotoelectric transfer efficiency can be obtained from the coatingliquid for forming a metal oxide semiconductor film for use in aphotoelectric cell according to the present invention.

EXAMPLES

The present invention will be further illustrated below with referenceto the following Examples, which in no way limit the scope of theinvention.

Example 1

5 g of titanium hydride was suspended in 1 lit. of pure water, 400 g ofa hydrogen peroxide solution of 5% by weight concentration was added tothe suspension over a period of 30 min, and heated to 80° C. to effectdissolution. Thus, a solution of peroxotitanic acid was obtained. 90% byvolume was divided from the whole amount of the solution, and its pH wasadjusted to 9 by adding concentrated aqueous ammonia. The resultantmixture was placed in an autoclave and subjected to a hydrothermaltreatment at 250° C. for 5 hr under saturated vapor pressure. Thus,titania colloid particles were obtained. The obtained titania colloidparticles were analyzed by X-ray diffractometry. As a result, it wasfound that they consisted of highly crystalline anatase titanium oxide.The crystallite diameter and average particle diameter of the titaniacolloid particles are listed in Table 1.

Subsequently, the obtained titania colloid particles were concentratedto a concentration of 10% by weight and mixed with the peroxotitanicacid solution. Hydroxypropylcellulose as a film formation auxiliary wasadded to the mixture in an amount of 30% by weight based on the titaniumcontents, in terms of TiO₂, of the mixture. Thus, a coating liquid forforming a semiconductor film was obtained.

Thereafter, this coating liquid was applied onto a transparent glassplate covered with a transparent electrode layer of fluoride-doped tinoxide on the side of the transparent electrode layer, and then coatingfilm was air-dried and irradiated with 6000 mJ/cm² ultraviolet light bymeans of a low pressure mercury lamp. Thus, the peroxotitanic acid wasdecomposed and the coating film was hardened. The coating film washeated at 300° C. for 30 min to thereby carry out hydroxypropylcellulosedecomposition and annealing. Thus, a metal oxide semiconductor film wasformed.

With respect to the formed metal oxide semiconductor film, the filmthickness and the pore volume and average pore diameter measured by thenitrogen adsorption technique are listed in Table 1.

Adsorption of Photosensitizer

A ruthenium complex of cis-(SCN⁻)-bis(2,2′-bipyridyl-4,4′-dicarboxylato) ruthenium (II) as a photosensitizerwas dissolved in ethanol in a concentration of 3×10⁻⁴ mol/lit. The thusobtained photosensitizer solution was applied onto the metal oxidesemiconductor film by the use of 100 rpm spinner, and dried. Theseapplication and drying operations were repeated five times. Thephotosensitizer adsorption amount of the obtained metal oxidesemiconductor film is listed in Table 1.

Preparation of Photoelectric Cell

Acetonitrile and ethylene carbonate were mixed together in a volumeratio (acetonitrile:ethylene carbonate) of 1:4 to thereby obtain asolvent. Tetrapropylammonium iodide and iodine were dissolved inrespective concentrations of 0.46 and 0.06 mol/lit. in the solvent tothereby obtain an electrolyte solution.

The above obtained electrode on glass plate, as one electrode, and atransparent glass plate covered with an electrode of fluoride-doped tinoxide having platinum superimposed thereon, as a counter electrode, werearranged so that the one electrode and the counter electrode wereopposite to each other. The sides thereof were sealed with a resin, andthe above electrolyte solution was charged so as to lie between the twoelectrodes. These electrodes were electrically connected to each otherby a lead. Thus, a photoelectric cell was obtained.

The photoelectric cell was irradiated with light of 100 W/m² intensityby means of a solar simulator. The Voc (voltage in open circuitcondition), Joc (density of current flowing at a short circuit),FF(curve factor) and η (transfer efficiency) were measured.

The results are given in Table 1.

Example 2

A metal oxide semiconductor film was produced in the same manner as inExample 1, except that, after the peroxotitanic acid decomposition andfilm hardening by ultraviolet irradiation, Ar gas ion irradiation wascarried out (irradiated at 200 eV for 10 hr with the use of ionimplanter manufactured by Nissin Electric Co., Ltd.).

The pore volume and average pore diameter of the obtained metal oxidesemiconductor film are listed in Table 1.

Adsorption of Photosensitizer

An adsorption of photosensitizer on the obtainable titanium oxide filmwas performed in the same manner as in Example 1.

The adsorption amount of photosensitizer is listed in Table 1.

Preparation of Photoelectric Cell

A photoelectric cell was prepared in the same manner as in Example 1,and the Voc, Joc, FF and η thereof were measured.

The results are given in Table 1.

Example 3

18.3 g of titanium tetrachloride was diluted with pure water, therebyobtaining an aqueous solution of 1.0% by weight concentration in termsof TiO₂. Aqueous ammonia of 15% by weight concentration was added to theaqueous solution under agitation, thereby obtaining a white slurry of pH9.5. This slurry was filtered and washed, thereby obtaining a cake oftitanium oxide hydrate gel of 10.2% by weight in terms of TiO₂. Thiscake was mixed with 400 g of a hydrogen peroxide solution of 5%concentration, and heated to 80° C. to thereby effect dissolution. Thus,a solution of peroxotitanic acid was obtained. 90% by volume was dividedfrom the whole amount of the solution, and its pH was adjusted to 9 byadding concentrated aqueous ammonia. The resultant mixture was placed inan autoclave and subjected to a hydrothermal treatment at 250° C. for 5hr under saturated vapor pressure. Thus, titania colloid particles wereobtained. The obtained titania colloid particles were analyzed by X-raydiffractometry, and it was found that they consisted of highlycrystalline anatase titanium oxide. The crystallite diameter and averageparticle diameter of the obtained particles are listed in Table 1.

From the obtained peroxotitanic acid solution and titania colloidparticles, a metal oxide semiconductor film was formed in the samemanner as in Example 1. The thickness, pore volume and average porediameter of the obtained metal oxide semiconductor film are listed inTable 1.

Adsorption of Photosensitizer

An adsorption of photosensitizer was performed in the same manner as inExample 1. The photosensitizer adsorption amount of the obtained metaloxide semiconductor film is listed in Table 1.

Preparation of Photoelectric Cell

A photoelectric cell was prepared in the same manner as in Example 1,and the Voc, Joc, FF and η thereof were measured. The results are givenin Table 1.

Comparative Example 1

18.3 g of titanium tetrachloride was diluted with pure water, therebyobtaining an aqueous solution of 1.0% by weight concentration in termsof TiO₂. Aqueous ammonia of 15% by weight concentration was added to theaqueous solution under agitation, thereby obtaining a white slurry of pH9.5. This slurry was filtered and washed, and suspended in pure water tothereby obtain a slurry of titanium oxide hydrate gel of 0.6% by weightconcentration in terms of TiO₂. The pH of the slurry was adjusted to 2by adding hydrochloric acid. The resultant slurry was placed in anautoclave and subjected to a hydrothermal treatment at 180° C. for 5 hrunder saturated vapor pressure. Thus, titania colloid particles wereobtained. The crystal form of the obtained particles was analyzed byX-ray diffractometry, and it was found that the particles wereamorphous. The average particle diameter of the titania colloidparticles is listed in Table 1.

Subsequently, the obtained titania colloid particles were concentratedto a concentration of 10% by weight. Hydroxypropylcellulose as a filmformation auxiliary was added thereto in an amount of 30% by weight interms of TiO₂. Thus, a coating liquid for forming a semiconductor filmwas obtained. Thereafter, this coating liquid was applied onto atransparent glass plate covered with an electrode layer offluoride-doped tin oxide on the side of the electrode layer, and thenthe coating film was air-dried and irradiated with 6000 mJ/cm²ultraviolet light by means of a low pressure mercury lamp. Thus, thecoating film was hardened. The coating film was heated at 300° C. for 30min to thereby carry out hydroxypropylcellulose decomposition andannealing. Thus, a metal oxide semiconductor film was formed.

With respect to the formed metal oxide semiconductor film, the filmthickness and the pore volume and average pore diameter measured by thenitrogen adsorption technique are listed in Table 1.

Adsorption of Photosensitizer

An adsorption of photosensitizer was performed in the same manner as inExample 1. The photosensitizer adsorption amount of the obtained metaloxide semiconductor film is listed in Table 1.

Preparation of Photoelectric Cell

A photoelectric cell was prepared in the same manner as in Example 1,and the Voc, Joc, FF and η thereof were measured.

The results are given in Table 1.

Comparative Example 2

Titania colloid particles obtained in the same manner as in Example 1were dried and annealed at 550° C. for 2 hr, thereby obtaining titaniaparticles. The obtained titania particles were analyzed by X-raydiffractometry, and it was found that they consisted of rutile titaniumoxide in which anatase titanium oxide was mixed. The crystallitediameter and average particle diameter of the obtained particles arelisted in Table 1.

Subsequently, a 10% by weight dispersion of the obtained titaniaparticles was prepared and mixed with the above peroxotitanic acidsolution. Hydroxypropylcellulose as a film formation auxiliary was addedthereto in an amount of 30% by weight based on the titanium contents, interms of TiO₂, of the mixture. Thus, a coating liquid for forming asemiconductor film was obtained.

Thereafter, this coating liquid was applied onto a transparent glassplate covered with an electrode layer of fluoride-doped tin oxide on theside of the electrode layer, and then the coating film was air-dried andirradiated with 6000 mJ/cm² ultraviolet light by means of a low pressuremercury lamp. Thus, the peroxotitanic acid was decomposed and thecoating film was hardened. The coating film was heated at 300° C. for 30min to thereby carry out hydroxypropylcellulose decomposition andannealing. Thus, a metal oxide semiconductor film was formed.

With respect to the formed metal oxide semiconductor film, the filmthickness and the pore volume and average pore diameter measured by thenitrogen adsorption technique are listed in Table 1.

Adsorption of Photosensitizer

An adsorption of photosensitizer was performed in the same manner as inExample 1. The photosensitizer adsorption amount of the obtained metaloxide semiconductor film is listed in Table 1.

Preparation of Photoelectric Cell

A photoelectric cell was prepared in the same manner as in Example 1,and the Voc, Joc, FF and η thereof were measured.

The results are given in Table 1.

TABLE 1 Titanium oxide colloid Semiconductor film particles Adsorptiondiam. of av. thickness amt. of Photoelectric cell crystal- particle ofav. pore photo- Joc crystal lite diam. film pore vol. diam. sensitizerVoc (mA/ η form (nm) (nm) (μm) (nm) (nm) (μg/cm²) (V) cm²) FF (%)Example 1 anatase 30 40 12 0.6 18 200 0.71 1.47 0.72 7.5 Example 2anatase 30 40 12 0.6 18 230 0.73 1.45 0.73 7.7 Example 3 anatase 13 15 90.5 10 150 0.64 1.48 0.70 6.6 Comp. Ex. amorphous —  4 7 0.3 6 160 0.551.40 0.40 1.8 1 Comp. Ex. rutile *1 5 45 12 0.6 28 110 0.60 1.60 0.422.0 2 *1 partly containing a minute amount of anatase.

Example 4

Preparation of Coating Liquid

5 g of titanium hydride was suspended in 1 lit. of pure water, 400 g ofa hydrogen peroxide solution of 5% by weight concentration was added tothe suspension over a period of 30 min, and heated to 80° C. to effectdissolution. Thus, a solution of peroxotitanic acid was obtained. 90% byvolume was divided from the whole amount of the solution, and its pH wasadjusted to 9 by adding concentrated aqueous ammonia. The resultantmixture was placed in an autoclave and subjected to a hydrothermaltreatment at 250° C. for 5 hr under saturated vapor pressure. Thus,titania colloid particles were obtained. The obtained titania colloidparticles were analyzed by X-ray diffractometry, and it was found thatthey consisted of highly crystalline anatase titanium oxide. The averageparticle diameter of the titania colloid particles is listed in Table 2.

Subsequently, the obtained titania colloid particles were concentratedto a concentration of 10% by weight and mixed with the peroxotitanicacid solution. Hydroxypropylcellulose as a film formation auxiliary wasadded to the mixture in an amount of 30% by weight based on the titaniumcontents, in terms on TiO₂, of the mixture. Thus, a coating liquid forforming a metal oxide semiconductor layer was obtained.

Formation of Electrode

A 5 μm thick film of fluoride-doped tin oxide was formed on one side ofa transparent glass plate by means of magnet sputtering apparatus(HSR-521A manufactured by Shimadzu Corporation) with the use of a targetof fluoride-doped tin oxide under conditions such that RE power: 500 W,Ar gas: 10 sccm, pressure: 0.04 torr, time: 200 min, and platetemperature: 250° C. Subsequently, resist (OFPR-800 produced by TokyoOhka Kogyo Co., Ltd.) was applied onto the film of fluoride-doped tinoxide, and 2 μm-pitch line & space patterning was performed. Thereafter,etching was carried out by means of reactive ion etching RIE apparatus(DEM451T manufactured by Anelva Corporation) under conditions such thatRF power: 500 W and mixed gas of BCl₃ (40 sccm) and Ar gas (10 sccm): 10Pa. The resist was removed by ashing. Thus, there were formed a 0.5 μmthick transparent electrode layer and 4.5 μm high transparent conductiveprotrusions.

A 0.5 μm thick layer of fluoride-doped tin oxide was formed on one sideof another transparent glass plate by means of the same magnetsputtering apparatus (HSR-521A) with the use of a target offluoride-doped tin oxide under conditions such that RF power: 500 W, Argas: 10 sccm, pressure: 0.04 torr and time: 20 min. This layer wascovered with platinum, thereby forming an electrode layer.

Thereafter, the above prepared coating liquid for forming a metal oxidesemiconductor layer was applied onto the conductive protrusions andtransparent electrode layer of fluoride-doped tin oxide, air dried andirradiated with 6000 mJ/cm² ultraviolet light by means of a low pressuremercury lamp. Thus, the peroxotitanic acid was decomposed and the layerwas hardened. The layer was heated at 300° C. for 30 min to therebycarry out hydroxypropylcellulose decomposition and annealing. Thus, atitanium oxide semiconductor layer having a flat metal oxidesemiconductor layer surface was formed.

With respect to the formed titanium oxide semiconductor layer, the layerthickness and the pore volume and average pore diameter measured by thenitrogen adsorption technique are listed in Table 2.

Adsorption of Photosensitizer

A ruthenium complex of cis-(SCN⁻)-bis(2,2′-bipyridyl-4,4′-dicarboxylato) ruthenium (II) as a photosensitizerwas dissolved in ethanol in a concentration of 3×10⁻⁴ mol/lit. The thusobtained photosensitizer solution was applied onto the titanium oxidesemiconductor layer by the use of 100 rpm spinner, and dried. Theseapplication and drying operations were repeated five times. Thephotosensitizer adsorption amount, per cm² of specific surface area ofthe titanium oxide semiconductor layer, of the obtained titanium oxidesemiconductor layer is listed in Table 2.

First, acetonitrile and ethylene carbonate were mixed together in avolume ratio of 1:4 to thereby obtain a solvent. Tetrapropylammoniumiodide and iodine were dissolved in respective concentrations of 0.46and 0.06 mol/lit. in the solvent to thereby obtain an electrolytesolution.

The above obtained transparent glass plate provided with electrode layerand conductive protrusions, as one electrode, and the above obtainedtransparent glass plate provided with electrode layer, as a counterelectrode, were arranged so that the one electrode and the counterelectrode were opposite to each other. The sides thereof were sealedwith a resin, and the above electrolyte solution was charged so as tolie between the two electrodes. These electrodes were electricallyconnected to each other by a lead. Thus, photoelectric cell wasobtained.

The obtained photoelectric cell was irradiated with light of 100 W/m²intensity by means of a solar simulator, and the Voc, Joc, FF and ηthereof were measured.

The results are given in Table 2.

Example 5

The coating liquid for forming a metal oxide semiconductor layer,prepared in Example 4, was diluted with water so that the concentrationthereof became ⅓, thereby obtaining the desired coating liquid forforming a metal oxide semiconductor layer (titania colloid particlesprepared in Example 4 were contained in a concentration of 3.3% byweight, and hydroxypropylcellulose was contained in an amount of 10% byweight based on the titanium contents, in terms of TiO₂, of the liquid).

The thus obtained coating liquid for forming a metal oxide semiconductorlayer was applied onto conductive protrusions and electrode layercomposed of fluoride-doped tin oxide as described in Example 4 andrapidly dried. These operations were repeated six times. As a result, atitanium oxide semiconductor layer having a portion of the electrolyteinfiltrated in the metal oxide semiconductor layer as described inExample 4 was formed.

Thereafter, the titanium oxide semiconductor layer was irradiated with6000 mJ/cm² ultraviolet light by means of a low pressure mercury lamp.Thus, the peroxotitanic acid was decomposed and the titanium oxidesemiconductor layer was hardened. Further, the titanium oxidesemiconductor layer was heated at 300° C. for 30 min to thereby carryout hydroxypropylcellulose decomposition and annealing. Thus, a titaniumoxide semiconductor layer having a flat metal oxide semiconductor layersurface was formed.

With respect to the formed titanium oxide semiconductor layer, the layerthickness and the pore volume and average pore diameter measured by thenitrogen adsorption technique are listed in Table 2.

Adsorption of Photosensitizer

An adsorption of photosensitizer on the titanium oxide layer wasperformed in the same manner as in Example 4.

The adsorption amount of photosensitizer is listed in Table 2.

Preparation of Photoelectric Cell

A photoelectric cell was prepared in the same manner as in Example 4,and the Voc, Joc, FF and η thereof were measured. The results are givenin Table 2.

Example 6

Preparation of Particles Having Core-Shell Structure

A solution consisting of a mixture of 7.6 g of tetraethoxysilane and 100g of ethanol was added once to a solution consisting of a mixture of 200g of ethanol, 25 g of pure water and 60 g of aqueous ammonia of 29% byweight concentration. Thus, a dispersion of spherical silica particleshaving an average particle diameter of 0.2 μm was obtained. The obtaineddispersion was concentrated to a silica concentration of 10% by weightby means of a rotary evaporator, thereby obtaining a silica particledispersion (core particles).

5.5 g of titanium hydride was suspended in 1 lit. of pure water, 400 gof a hydrogen peroxide solution of 5% by weight concentration was addedto the suspension over a period of 30 min, and heated to 80° C. toeffect dissolution. Thus, a solution of peroxotitanic acid was obtained.

The previously prepared silica particle dispersion was heated to 90° C.,and the peroxotitanic acid solution was added thereto over a period of100 hr. Thus, there was obtained a dispersion of metal oxide particlesconsisting of a core of silica and a shell of titanium oxide. Theobtained metal oxide particles were analyzed by X-ray diffractometry,and it was found that the shell consisted of anatase titanium oxide. Theaverage particle diameter of the metal oxide particles is listed inTable 2.

Preparation of Photoelectric Cell

A 0.5 μm thick electrode layer of fluoride-doped tin oxide was formed onone side of a transparent glass plate 5 by means of magnet sputteringapparatus (HSR-521A manufactured by Shimadizu Corporation) with the useof a target of fluoride-doped tin oxide under conditions such that RFpower: 500 W, Ar gas: 10 sccm, pressure: 0.04 torr, and time: 20 min.

A 0.5 μm thick layer of fluoride-doped tin oxide was formed on one sideof another transparent glass plate by means of magnet sputteringapparatus (HSR-521A manufactured by Shimadzu Corporation) with the useof a target of fluoride-doped tin oxide under conditions such that RFpower: 500 W, Ar gas: 10 sccm, pressure: 0.04 torr and time: 20 min.This layer was covered with platinum, thereby forming an electrodelayer.

Negative-type photoresist (OMR-83 produced by Tokyo Ohka Kogyo Co.,Ltd.) was applied onto the electrode layer 1 by 500 rpm spin coating,thereby forming a 6 μm thick resist film. Aligner exposure andsubsequent development of the photoresist were carried out, and 6μm-pitch line & space patterning was performed.

Thereafter, the transparent glass plate furnished with the patternedelectrode layer was immersed in a dispersion of metal oxide particles.Using a platinum electrode as a counter electrode, a positive voltagewas applied to the transparent glass plate. Thus, inter-resistdeposition of metal oxide particles was effected. A separately preparedperoxotitanic acid was applied onto the layer of metal oxide particlesby spin coating in an oxide weight ratio of 0.15 to the metal oxideparticles, air dried, and irradiated with 6000 mJ/cm² ultraviolet lightby means of a low pressure mercury lamp. Thus, the peroxotitanic acidwas decomposed and the metal oxide semiconductor layer was hardened.

After the hardening, the resist was removed by O²-ashing. Subsequently,a dispersion of indium colloid particles (ARS-22A with a particlediameter of 0.07 μm and a concentration of 2.5% by weight, produced byCatalysts & Chemicals Industries Co., Ltd.) was applied by spin coatingso that the portions freed of the resist were packed with indium colloidparticles to the same height as that of the metal oxide particle layer.Thus, conductive protrusions were formed.

The peroxotitanic acid solution was mixed with a metal oxide particledispersion of 10% concentration obtained in the same manner as mentionedabove in an oxide weight ratio of 0.15 to the metal oxide particles.Hydroxypropylcellulose as a film formation auxiliary was added to themixture in an amount of 30% by weight based on the weight of metal oxidecontained in the mixture. Thus, a coating liquid for forming a metaloxide semiconductor layer was obtained. This coating liquid was appliedonto the metal oxide particle layer and the conductive protrusionscomposed of indium colloid particles, air dried once more, andirradiated with 6000 mJ/cm² ultraviolet light by means of a low pressuremercury lamp. Thus, peroxotitanic acid decomposition and hardening wereeffected. Further, heating was performed at 300° C. for 30 min tothereby carry out hydroxypropylcellulose decomposition and annealing.Thus, a titanium oxide semiconductor layer having a flat metal oxidesemiconductor layer surface was formed.

With respect to the formed titanium oxide semiconductor layer, the layerthickness and the pore volume and average pore diameter measured by thenitrogen adsorption technique are listed in Table 2.

Adsorption of Photosensitizer

An adsorption of photosensitizer on the metal oxide semiconductor layerwas performed in the same manner as in Example 4. The adsorption amountof photosensitizer is listed in Table 2.

Preparation of Photoelectric Cell

A photoelectric cell was prepared in the same manner as in Example 1,and the Voc, Joc, FF and η thereof were measured.

The results are given in Table 2.

TABLE 2 Titanium oxide colloid particles av. part- diam. of icleConductive protrusions crystal crstallite diam. configu- height widthinterval form (nm) (nm) ration (μm) (μm) (μm) Example anatase 30  35Cuboid 4.5 2 2 4 struct- ure Example anatase 30  35 Cuboid 4.5 2 2 5struct- ure Example anatase 13 300 Cuboid 6   6 6 6 *2 struct- ureSemiconductor layer thickness of semi- conductor layer on adsorpt-conductive ion amt. Photoelectric thickness protrusion of photo- cell oflayer or elect- av. pore sensit- Joc per se rode layer pore vol. diam.izer Voc (mA/ η (μm) (μm) (nm) (nm) (μg/cm²) (V) cm²) FF (%) Example11.5   7-11.5 0.6  18 200 0.63 1.67 0.72 7.6 4 Example 8.5-14.5  8-100.6  18 200 0.64 1.75 0.74 8.3 5 Example 9  3-9 0.4 120 180 0.68 1.810.70 8.6 6 *2 comprising silica particles as cores.

What is claimed is:
 1. A photoelectric cell comprising: a firstinsulating base having on its surface a first electrode layer, saidfirst electrode layer having on its surface a metal oxide semiconductorlayer on which a photosensitizer is adsorbed; a second insulating basehaving on its surface a second electrode layer, said first electrodelayer and said second electrode layer arranged opposite to each other;and an electrolyte sealed between the metal oxide semiconductor layerand the second electrode layer, wherein: conductive protrusions juttingfrom the surface of the first electrode layer exist, said metal oxidesemiconductor layer formed so as to cover the conductive protrusions andthe first electrode layer, and at least one of said first insulatingbase having an electrode layer and said second insulating base having anelectrode layer is transparent.
 2. The photoelectric cell as claimed inclaim 1, wherein the metal oxide semiconductor layer is formed along acontour of the conductive protrusions.
 3. The photoelectric cell asclaimed in claim 1, wherein the metal oxide semiconductor layercomprises spherical particles of at least one of metal oxides selectedfrom the group consisting of titanium oxide, lanthanum oxide, zirconiumoxide, niobium oxide, tungsten oxide, strontium oxide, zinc oxide, tinoxide and indium oxide.
 4. The photoelectric cell as claimed in claim 3,wherein the spherical particles have an average particle diameterranging from 5 to 600 nm.
 5. The photoelectric cell as claimed in claim4, wherein the spherical particles are composed of anatase titaniumoxide.
 6. The photoelectric cell as claimed in claim 4, wherein thespherical particles are those having a core-shell structure comprising acore particle of 0.1 to 500 nm in average particle diameter having itssurface covered with a shell.
 7. The photoelectric cell as claimed inclaim 6, wherein the shell of the spherical particles of the core-shellstructure is composed of anatase titanium oxide.
 8. The photoelectriccell as claimed in claim 5, wherein the anatase titanium oxide is oneobtained by subjecting peroxotitanic acid to heating and aging.
 9. Thephotoelectric cell as claimed in claim 2, wherein the metal oxidesemiconductor layer comprises spherical particles of at least one ofmetal oxides selected from the group consisting of titanium oxide,lanthanum oxide, zirconium oxide, niobium oxide, tungsten oxide,strontium oxide, zinc oxide, tin oxide and indium oxide.
 10. Thephotoelectric cell as claimed in claim 6, wherein the anatase titaniumoxide is one obtained by subjecting peroxotitanic acid to heating andaging.
 11. The photoelectric cell as claimed in claim 1, wherein themetal oxide semiconductor layer contains a titanium oxide binder. 12.The photoelectric cell as claimed in claim 1, wherein the metal oxidesemiconductor layer is one obtained by implanting ions of at least onegas selected from the group consisting of O₂, N₂, H₂ and inert gases ofGroup 0 of the periodic table and thereafter annealing.
 13. Thephotoelectric cell as claimed in claim 1, wherein the metal oxidesemiconductor layer has a pore volume of 0.05 to 0.8 ml/g and an averagepore diameter of 2 to 250 nm.
 14. A process for producing a metal oxidesemiconductor film for use in a photoelectric cell, comprising applyinga coating liquid comprised of peroxotitanic acid, anatase titanium oxideparticles and a dispersion medium to obtain a coating film and curingthe coating film, wherein the coating film is cured by irradiating thecoating film with ultraviolet light irradiation, subsequently subjectingthe coating film to implantation of ions of at least one gas selectedfrom the group consisting of O₂, N₂, H₂ and inert gases of Group 0 ofthe periodic table and thereafter annealing.